As a conventional optical recording medium there are optical discs, that is, so-called ROM (Read-Only Memory) type discs used only for reproduction such as CDs (Compact Discs) and DVDs (Digital Versatile Discs), for audio, game program and other uses.
Information recording on such optical recording medium is performed by forming a recording portion recorded as changes in physical shape in the thickness direction or in the track width direction, for example, pits and lands or meandering guide grooves or similar, and also a reflective film of an Al film or similar is deposited such that the information in these recording portions can be read optically with a high SNR (signal-to-noise ratio).
An optical recording medium having a recording portion with such changes in physical shape affords the advantage that manufacturing can be performed inexpensively in large volumes, since for example injection molding is used to form the plastic substrate and at the same time forms the recording portion, or that the recording portion is formed by the 2P method (photopolymerization method) on for example plastic substrate.
Hence in this type of an optical recording medium, there is the problem of replication by routes other than the formal one, for example, replication without obtaining the consent of copyright holders.
Because this optical recording medium is read in a non-contact manner, and there is almost no degradation of characteristics due to repeated use, sales may take place through non-normal routes such that used articles are sold as new articles and similar cases, so that in a similar manner the problem of sales without the consent of the copyright holders may occur.
Hence there is a desire to be able to record, in such types of an optical recording medium, a code, mark or similar as means for discriminating by the manufacturer whether, for example, the article has passed through normal routes.
Further, it is desired that, for example in game applications, it be possible to perform recording sufficient to judge the ending point where a user interrupts and ends a game, and that it be possible to easily record personal information for the user and similar on the user side.
Also, manufacturers and users desire a function enabling correction of a portion of the data accumulated on a disc, or enabling partially adding of new data, after the disc is manufactured. Taking car navigation applications as an example, through addition of the above-described function, simply map modifications and added information could be transmitted from the manufacturer, or data could be obtained by the user himself, and recorded on the disc on the user side.
An optical recording medium enabling conventional optical recording, that is, a write-once optical recording medium and a rewritable optical recording medium, conventionally are constructed from a recording film, comprising recording material the optical characteristics of which change upon irradiation by a recording laser, and a reflective film comprising material with high reflectivity.
A write-once optical recording medium, such as for example a CD-R medium to which writing is possible only once, is fabricated by coating a plastic substrate having guide grooves with a dye material using a spin-coating method, after which a metal thin film of Au or another material with high reflectivity is formed by sputtering.
A rewritable magneto-optical recording medium is fabricated by sequentially sputtering, on a plastic substrate in which are formed guide grooves, a transparent dielectric film, a perpendicular magnetization film of TbFeCo or other recording material, a transparent dielectric film, and an Al reflective film.
Further, a rewritable phase-change recording medium is constructed using GeSbTe or another phase-change material as the recording material in the above-described rewritable optical recording medium.
However, all of these recording materials are expensive, and because of the need to form numerous films in a rewritable optical recording medium as described above, there are a large number of manufacturing processes; when these recording materials are used to form a additional recording layer, costs are much higher than for the above-described CDs or other ROM-type optical recording media.
In addition, by using a write-once optical recording medium constructed with a single layer of AuSn or AuSnTi thin film or TeO thin film as the recording film, or a single-layer film of GeSbTe or similar used in phase-change recording, it is possible to construct an optical recording medium which, even employing only a single layer, enables additional recording; however these materials also are expensive to pose a problem.
Hence inventors of the present invention and others have proposed an optical recording medium constructed to enable additional data recording, using a semiconductor laser having ordinary output, in film in which Ge, Ti, Ni, Si, Tb, Fe, Ag or similar is added in a specific amount to Al.
However, when additionally recording data to such film, due to fluctuations in the sputtering deposition conditions and in the composition of the target used in sputtering, or to fluctuations in the thickness of the film formed, the laser power necessary for optical writing to the film may fluctuate, and as a result there is the problem that stable recording cannot be performed.
In order to resolve the above-described problems, in this invention an optical recording medium which can be manufactured inexpensively due to a construction and manufacturing method corresponding to the construction of a read-only optical recording medium, which enables the additional recording of the above-described codes, marks, and other new information, and which has satisfactory characteristics enabling stable recording, as well as a manufacturing method thereof, an optical recording method, an optical reproducing method, an optical recording device, an optical reproducing device, and an optical recording and reproducing device are provided.